-Disclaimer-
I do not own and am not making any profit off these covers, nor do I own the majority of the visuals.
The covered songs are credited on the page. 

BeepBox is developed by John Nesky, 
also known as @Shaktool: https://twitter.com/shaktool

Visuals:
Undertale - S.1: Sprites from the original game.
Undertale - S.2: Sprites from the original game.
Undertale - S.3: Sprites from the original game.
Vim - No - Src: https://www.youtube.com/watch?v=MBDJEcTLrKI
Undertale - S.4: Fan-art by Seven-Bit on Deviantart: https://www.deviantart.com/seven-bit/art/Fallen-Down-Undertale-654631476
Undertale - S.5: Fan-art by Mnstrcndy/MC/Kay on tumblr: http://mnstrcndy.tumblr.com/post/162601443319/visual-development-and-background-for-the
Undertale - S.6: Sprites mashup from the original game.
Undertale - S.6: Just the fighting-grid from Undertale made in photoshop.
Groovy Birthday: cover of the "Happy Birthday" song, and the background is from the Pokemon Anime.
Castlevania - Vampire Killer: A tiled sprite from CastleVania.
Undertale - S.8: Sprites from the original game.
Undertale - S.9: Just the fighting-grid from Undertale made in photoshop.
Undertale - S.10: Sprites from the original game.
Undertale - S.11: Sprites from the original game.
Undertale - S.12: Sprites from the original game.
Undertale - S.13: Scene from the original game, shading by gzorro20 on Deviantart: https://www.deviantart.com/gzorro20/art/Home-590416799
Undertale - S.15: Fan-art by Seven-Bit on Deviantart: http://mnstrcndy.tumblr.com/post/143048902064/out-of-the-cold
Undertale - S.16: Scene from the original game.
Undertale - S.18: Fan-art by Mnstrcndy/MC/Kay on tumblr: http://mnstrcndy.tumblr.com/
Undertale - S.20: Fan-art by Mnstrcndy/MC/Kay on tumblr: http://mnstrcndy.tumblr.com/
Undertale - S.22: Fan-art by Mnstrcndy/MC/Kay on tumblr: http://mnstrcndy.tumblr.com/
Undertale - S.22: Fan-art by Mnstrcndy/MC/Kay on tumblr: http://mnstrcndy.tumblr.com/
Undertale - S.23: Background sprite from the original game.
Undertale - S.30: Sprites from the original game.
Undertale - S.32: Sprites from the original game.
Undertale - S.35: Gif recorded from the original game.
Undertale - S.37: Background sprite from the original game.
Undertale - S.38: Background sprite from the original game, with a grey filter.
Undertale - S.39: Background sprite from the original game, with more filters.
Undertale - S.40: Sprites from the original game.
Undertale - S.42: Screenshot from the original game.
Undertale - S.43: Screenshot from the original game.
Undertale - S.44: Background sprite from the original game.
Undertale - S.48: Background sprites edited together the original game.
Undertale - S.48: Background sprites edited together the original game.
Undertale - S.49: Fan-animation by Gooseworx on Deviantart: https://www.deviantart.com/gooseworx/art/It-s-Showtime-597724796
Undertale - S.67: Sprite from the original game.
Undertale - S.68: Gif recorded from the original game.
Binding of Isaac - Theme: Binding of Isaac Wrath of the Lamb - Steam Background: https://steamcommunity.com/market/listings/753/113200-Wrath%20of%20the%20Cast
Starwars - Cantina Band: Gif recorded from Star Wars Episode 1.
Scott Pilgrim vs. The World: Subboss Theme: Wallpaper made of a scan from volume 1 of Scott Pilgrim comics: https://www.deviantart.com/quiklost/art/Scott-Pilgrim-Wallpaper-167636333
Snapshot OST - Knowing the Meaning: Screenshot from the original game.
Pangolin Love - Cutscene from the original game made into a gif.
Spore - Flower Dance: Wallpaper from the original game.
Cortex Command - This World: Screenshot of the game's title screen.
Crash Bandicoot Wrath Of Cortex - Theme: Gif recording of the loading screen from the original game.
Neil Cicierega - BRODYQUEST: Background from idevie tutorials: https://idevie.com/tutorials/create-a-realistic-star-field-with-space-dust-in-photoshop-with-action . Adrien Brody GIF: Adrien Brody.
Super Hexagon - Hexagon Stage: Gif from the Super Hexaon remake "Meta Hexagon": https://gamebuino.com/creations/meta-hexagon
Bublby - World Bowser 8 Bit: bowser jump by Ivan/Pug-of-War: http://pug-of-war.tumblr.com/post/119430419251/bowser
Cave Story+ - On To Grasstown: Someone online didn't give them credit, but I know it's by someone from pixeljoint.com
Crypt of The Necrodancer - 3-2 Cold: Sprites from the original game.
Dubmood - 3D Galax: Screenshot from the original game.
VVVVVV - Background sprites put together from the original game.
Gigi D'Agostino - The Riddle: GIF recording from the music video, animation by FILM BILDER studios.
Rick Astley - Never Gonna Give You Up: GIF recording from the music video.
Undertale - S.100: Sprites from the original game and... another gif from the song above.
Discord (Remix) - The Living Tombstone
Super Mario Galaxy 2 - Puzzle Plank Galaxy: Wallpaper from the original game.
Harry Potter 1 Video Game - Happy Hogwarts: Screenshot from the original game.
Dubmood - LUCiD Keygen 2.xm: (I honestly don't know. Sorry!)
Syphus - Mia's Song.mod: Just a css gradient.
Crash Twinsanity - Rockslide Rumble: Art taken from two game over screens from the original game.
Vince Guaraldi Trio - Linus And Lucy: Gif recording from The Peanuts TV special: "A Charlie Brown Christmas".
Crypt of The Necrodancer - Lobby: Gif recording of the original game.
Portal 2 - Forwarding the Cause of Science: Wallpaper from the original game.
Jean Michel Jarre - Magnetic Fields 2: gif by Hexeosis on Tumblr: http://hexeosis.tumblr.com/post/170700674147
Smash Mouth - All Star: Movie poster of the movie.
Crypt of The Necrodancer: Sprites from the original game.
Chicken Invaders 2 - Theme (Just To Funk): Game Poster of the original game.
Harry Potter 3 - Aunt Marge's Waltz: Screenshot from Harry Potter and the Prisoner of Azkaban.
TheFatRat: Time Lapse: The album cover of TheFatRat's Single: Time Lapse https://thefatrat.bandcamp.com/track/time-lapse
Fez - Knowledge: Animated gif from the original game.
Angry Video Game Nerd II - Overworld: Sprites from the original game.
Rick and Morty - Theme: Pixel art by Mikołaj Birek: http://gallery.wacom.com/gallery/55883023/Rick-and-Morty-PIXEL-ART
Lumitrap - Through Ze Machine: Rube Goldberg Machine. Gif by hundreds of SomethingAwful forum goons.
Lumitrap - Detective Penguin: Illustration by Devin Hermanson: https://twitter.com/devinher
Undertale S.70: None
Pogemon Mystery Dungeon - Amp Plains: Art from the original game.
Dschinghis Khan - Moskau: Dance taunts from the game Team Fortress 2. Five Nights At Freddies model swap. Dragon dance: http://maguy69.centerblog.net/21560-danse-du-dragon
Legend of Zelda Breath of the Wild - Riding (Night): Wallpaper from the original game.
Waterflame - Electroman Adventures: Single cover.
Idle Tree Soundtrack - l3go: Sprites from the original game.
Oney Plays: Art by ChocolateCakeBag on DeviantArt: https://www.deviantart.com/chocolatecakebag/art/Oneyplays-desktop-wallpaper-650062028
Lumitrap/8372 - Electric Winds: https://gifer.com/en/9ZWy
Shovel Knight - Strike The Earth!: Background image from the game's own website.
Necrodancer - Fungal Funk: none.

/*Favicons*/
Sprites from respective games:
abe, amanita, bob, braid, crash, engi, goose, hexagon, isaac, papers, oeuf, pokeball, quack, scientist, shovel, slig, stanley, undernet, uplink, ut
discord, facebook
the picture of gabe newell has got to be public domain...

Website title font: Agit Prop by Sergey Kazakov https://www.dafont.com/agit-prop.font
World of Goo font: (well, similar enough). Earth's Mightiest by Iconian http://www.iconian.com/
Super Hexagon font: Bump IT UP - font by Graphic Designer Aaron Amar, CC Attribution Share Alike https://www.behance.net/aaronamar https://fontstruct.com/fontstructions/show/155156/bump_it_upg
Odd Font - The actual Oddworld font as it is used in (most) of the Oddworld games
Monster Friend - free font Designed by Harry Wakamatsu from Japan